My beloved dog "April" died unexpectedly today. My husband and I have decided to have an autopsy, but I really need to know what happened now. This is what happened.

April was a 10 yr spayed female sheppard mix, current on her shots. She was fine at her last annual check up. She had been acting a little strange over the past couple weeks. She did not appear ill, but was unusually aggressive toward people and pets that are not part of our family. She was her same sweet self with us. We attributed the behavior to grumpyness- she was old after all.

About a week ago, she refused to come when I called, which never happened before. I went to get her and, for a moment, she appeared reluctant to stand up and was very sad. The moment passed quickly and with a little affection, she was back to normal. I attributed her behavior to pouting. She was a very sensitive dog & I had scolded her earlier that day for killing a squirel in our yard.

She was just fine for the rest of the week until Sunday. We let her outside for a few hours in the morning - she loved to be outside in the early morning. When my husband called her to come in, she would not get up. He walked out in the yard expecting to find her guarding yet another squirel kill. Instead, he found that she was not able to get up. She could push herself up on her front paws, but her back legs & back seemed to be paralyzed. As we frantically dressed to take her to the afterhours pet ER, she managed to get up. She was able to walk, but her gate was stiff & she had a pronounced limp in her left hind leg.

She spent several hours at the pet ER where they did x-rays and ran tests for everything they could think of. The x-rays where fine ("hips of a 4 yr old") & other than low potassium, her blood work was as well. The Dr told us he believed she had a soft tissue injury, maybe a spraine & sent us home w/Dermaxx & instructions to keep her from being too active. He said to follow up with our vet if she didn't improve with the meds.

Monday & Tuesday day she seemed much better. She would seem more lathargic at night, but that seemed natural after a day of activity and the drugs she was on.

When my husband came home today, she did not greet him. He found her laying by our bed, unable to move at all. When he rushed out to get our very excited Lab out of the way, April got up and attempted to follow . She collapsed after a few steps and died a few minuites later while my husband was on the phone with the vet.

Can anyone tell me what may have happend, and if our 1 yr lab mix in now in danger?